1. Field of the Invention
The present invention relates to a semiconductor device (LSI) and, more specifically, to a semiconductor device having MISFET (metal insulator semiconductor field effect transistor).
2. Description of the Related Art
A conventional semiconductor device will be described by referring to FIG. 15. This semiconductor device is disclosed in Japanese Patent Unexamined Publication 2001-332706, for example. In this semiconductor device, the threshold voltage or the drive current is controlled by adjusting at least one of isolation widths in the gate length direction of an element isolation part which includes (or surrounds) an active region where MISFET is formed.
In this semiconductor device, as shown in FIG. 15, isolation width La of the element isolation part is relatively narrowed so as to increase an influence of the stress imposed upon a channel region of MISFET (Q2). Thereby, change of the threshold voltage is made relatively significant. Further, isolation width Lb of the element isolation part is relatively widened so as to decrease an influence of the stress imposed upon a channel region of MISFET (Q4). Thereby, change of the threshold voltage is made relatively insignificant.
However, there has been an issue in the semiconductor device that the area of the element in the semiconductor device becomes large since the stress imposed on the transistor region is controlled by the active region width and the element isolation width. An increase of the area as described above will be a demerit in the future where micronization of the semiconductor device will be going on and more reduction of the area are to be achieved. Recently, micronization has been achieved and an influence upon the transistor property which is caused by the stress to the channel region has been increased. Thus, conventionally, as disclosed in “T. Ghani, et al., IEEE, S11, p 6, 2003”, there is employed a method which improves the operating property of the transistor, e.g., the threshold voltage, drive current, by actively utilizing the stress which is generated during the process.